Search for Life
in the Solar System and Beyond
Abstract
This data story takes a general audience to appreciate the extraordinary fortune of finding life in the universe. For a more immersive experience, try reading in Morgan Freeman’s voice.
A world of extremes
To understand our Solar System can be quite challenging. For starters, our Solar System is huge. The Solar System is so big that kilometers are not very useful anymore. For the rest of our journey, we will be measuring distances with help of the speed of light (aprox. 300.000 km/s)
If we try to compare planets, we have to observe multiple dimensions simulatenously. For example, temperatures, distances or densities that are unique on every planet. This would require different magnitudes that are incompatible with eachother (°C, Km, …).
These measurements are very different from planet to planet. If we tried to represent the planets with their real proportions, it would be impossible for your screen to show everything. For this, it is more useful to create “planet signatures”.
As you can see in Figure 2, signatures are unique for each planet and based on normalised data. This way we can compare dimensions like millions of kilograms and other extreme measurements, even if we have one huge planet compared to a tiny moon.
Earth, a dwarf planet
Earth is stricktly speaking, a dwarf-planet. Jupiter is more than twice as massive than the other planets of our solar system combined. (Laboratory 2023)
Mercury is still shrinking
Mercury is already the smallest planet in the solar system and it’s only getting smaller and denser. (Vicky Stein 2022)
Venus is too hot
Venus’ thick atmosphere traps heat creating a runaway greenhouse effect. (Vicky Stein 2022)
Every planet is unique on its own way. Planets can be made of rock, metal, gas,… each with different densities. We believe that over millions of years, the Sun has attracted the heaviest particles on its way. As a result, we find small, heavy planets near the Sun, while the less dense and gigantic can be found on the edges of the solar system.
Planets may also have moons, rings or asteroids belts. In some planets rain is water, while in other it rains diamonds or molten metal! But the most special and rarest of all possible outcomes, is life!
Life is so unlikely that it is almost considered accidental.
Earth is a comfortable place for life
The only planet known to contain life is Earth. Life is the result of many improbable coincidences. The most remarkable is its distance from the Sun. This makes possible to find water just at the right temperature for life to thrive.
Our neighbours Mars and Venus, are a few “minutes” too close or far from the Sun. Mars’ water is permanently frozen, while Venus is hotter than a steamer pot.
Water world
There is water everywhere in the universe. However, it has to be liquid to sustain life (Vicky Stein 2022)
Backward Stinky Sunrise
Venus rotates backward on its axis, opposite to most planets in our solar system. Its sulfuric atmosphere smells like rotten eggs! (Lunar and Institute 2023)
Organic molecules are everywhere
Organics are complex carbon-based molecules found in living things, but which can be created by non-biological processes too (Vicky Stein 2022)
Supersonic winds!
Winds on Neptune can blow up to 1,500 miles per hour (2,400 km/h). Is all that energy coming from the sun, from the planet’s core, or gravitational contraction? Researchers are working to find out. (Vicky Stein 2022)
There are many other factors to enable life, and each of them is required. A little bit too much radiation and you are fried. Decrease the gravity and the athmospere would disolve. Even the slightest change in the polarity of Earth’s core and a solar storm would put and end to life.
This makes us the luckiest tenants in the solar system.
The Goldilocks
Habitable zones are also known as Goldilocks’ zones, where conditions might be just right – neither too hot nor too cold – for life. (“The Habitable Zone” 2021) But, how about beyond the Solar System? The so-called “Exoplanets”, are they “Earth-like”?
Exploring the vastness of our universe: exoplanets and their discovery methods
Our solar system is huge, as we have now seen. With today’s technologies we are able to get more information about the universe. Companies like NASA or ESA have been studying the universe for years and have made considerable progress in the last decades. But what exactly is the universe?
The universe and its exoplanets
The universe is unimaginably big. We know that the visible universe is about 93 billion light-years across. The universe is a vast expanse, filled with billions of galaxies, each containing billions of stars. A large collection of stars and other celestial bodies form a galaxy. The galaxy we live in is called the Milky Way. Our exploration of the cosmos has revealed that many of these stars have their own planetary systems, known as exoplanets. Discovering and understanding these distant worlds is a fascinating endeavor that expands our knowledge of the universe and the possibilities of life beyond our own solar system. (“Das Universum” 2022)
Exoplanet discovery methods
Scientists have developed various methods to detect and study exoplanets. Three prominent methods with already many discoveries of exoplanets are Transit, Radial Velocity and Microlensing:
Transit Method: A solar eclipse is one of the coolest astronomical events you’ll ever experience. It happens when the moon passes directly in front of the sun, blocking its light. This is similar to how the transit method finds exoplanets. When a planet passes directly between an observer and the star it orbits, it blocks some of that star’s light. For a brief period of time, that star actually gets dimmer. It’s a tiny change, but it’s enough to clue astronomers into the presence of an exoplanet around a distant star. (“Discovery Methods,” n.d.)
Radial Velocity Method: The planet causes the star to wobble around in its orbit, and as the planet moves to and fro, the light waves compress together and then stretch out, changing the color of the light we see. The radial velocity method was one of the first successful ways to find exoplanets, and continues to be one of the most productive methods. Often, this method will be used to confirm planets found with other methods - an extra step that can prove a planet exists. (“Discovery Methods,” n.d.)
Microlensing Method: Gravitational microlensing happens when a star or planet’s gravity focuses the light of another, more distant star, in a way that makes it temporarily seem brighter. In the same way that a magnifying glass can focus the sun’s light onto a tiny, very bright spot on a piece of paper, the gravity of the planet and the star focus the light rays of the distant star onto the observer. (“Discovery Methods,” n.d.)
These are the three main methods by which most exoplanets have been discovered over time. There are other less prolific methods not worth mentioning.
In Figure 4 you can see the the discovering-success by each method and the total count over the years.
Potentially habitable exoplanets
7 out of the top 10 most habitable exoplanets have been discovered by transit method
In search of habitable worlds: The top 10 most life-friendly exoplanets
Now that we have familiarized ourselves with the various methods used to discover exoplanets, let’s focus on the fascinating world of life-friendly exoplanets. The question of the existence of life outside our solar system holds a special fascination for us. Are there be other planets out there that have conditions similar to Earth’s and where life would be possible?
The habitability conditions that a planet must fulfill are not precisely known. However, it is comparatively easier to define conditions under which a planet is very likely inahbitable. Finding such conditions is important to select, which ones should be observed more detailed. A planet should have a maximum radius to fulfill two constraints
- Surface conditions compatible with the existence of liquid water
- No ice layer at the bottom of a global ocean
Results have shown that for planets similar to Earth in composition and within the Super Earth mass-range (1–12 times the mass of the Earth), the maximum radius that a planet can have varies between 1.7 and 2.2 times the radius of the Earth. (Alibert 2013)
Below in Figure 5 are the top 10 potentially habitable exoplanets, marked with their relative mass and radius compared to Earth. (Huber 2015) As you can see all top 10 exoplanets are within the ranges mentioned.
Gas giants
Gas giants are planets the size of Saturn or Jupiter, the largest planet in our solar system, or much, much larger. (“Planettypes” 2022)
Super Earth
Super Earths are typically terrestrial planets that may or may not have atmospheres. They are more massive than Earth, but lighter than Neptune. 9 out of the top 10 most habitable exoplanets are Super Earths. (“Planettypes” 2022)
Neptune-like
Neptunian planets are similar in size to Neptune or Uranus in our solar system. They likely have a mixture of interior compositions, but all will have hydrogen and helium-dominated outer atmospheres and rocky cores. (“Planettypes” 2022)
Terrestrial planets
Terrestrial planets are Earth-sized and smaller, composed of rock, silicate, water or carbon. Further investigation will determine whether some of them possess atmospheres, oceans or other signs of habitability. (“Planettypes” 2022)
Exo-Goldilocks
As we already have seen the definition of “habitable zone” Figure 3 is the distance from a star at which liquid water could exist on orbiting planets’ surfaces. (“The Habitable Zone” 2021)
Several factors play a role in ensuring that exoplanets have surface temperatures that are not too warm and not too cold. Two of them are the temperature of the host and its orbits radius (the radius to the star around which the planets orbit). How do the exoplanets compare to Earth and how far away are they?
As we can see in Figure 6 the top 10 most habitable exoplanets have similar properties in terms of orbital radius as Earth. Also the temperatures of their respective hosts are similar to the temperature of our sun.
Tau Ceti e: the nearest exoplanet with potential life
The journey to the nearest exoplanet Tau Ceti e would take about 22 years by spacecraft.
Astronomical unit AU
The astronomical unit is a unit of length, roughly the distance from Earth to the Sun and approximately equal to 150 million kilometres or 8.3 light-minutes. (“Astronomical Unit,” n.d.)
A matter of priorities
Whether life exists beyond Earth is one of the most profound questions of all time. The answer will change us forever, whether it reveals a universe rich with life, one in which life is rare and fragile, or even a universe in which we can find no other life at all. (“The Search for Life” 2020)
Nevertheless, these planets are at an unthinkable distance and it will be very difficult to colonize another planet. Our Earth is unique and is irreplaceable - we should take care of it!
Data, tools and inspiration:
- Planets data (Banerjee 2022)
- Planets data 2 (Lunar and Institute 2003)
- Exoplanet dataaset (Singh 2020)
- Radar charts (Libraries 2022)
- Dataviz catalogue (“Datavizcatalogue,” n.d.)
- Multiplots in plotly (RenaudLN, n.d.)
- Comparing Planet Volumes (polsci 2021)
- One level packed Circle (“Basic Circle Packing Chart” 2022)
- Cumulative Exoplanets Vizualization (“Visualization Cumulative Exoplanets, by Method” 2023)
- Top 10 potentially habitable exoplanets (Huber 2015)
References
Alibert, Y. 2013. “Visualization Cumulative Exoplanets, by Method.” https://www.aanda.org/articles/aa/abs/2014/01/aa22293-13/aa22293-13.html.
“Astronomical Unit.” n.d. https://en.wikipedia.org/wiki/Astronomical_unit#:~:text=The%20astronomical%20unit%20(symbol%3A%20au,)%20or%208.3%20light%2Dminutes.
Banerjee, Sourav. 2022. “Planet Dataset.” https://www.kaggle.com/datasets/iamsouravbanerjee/planet-dataset.
“Basic Circle Packing Chart.” 2022. https://www.python-graph-gallery.com/circular-packing-1-level-hierarchy/.
“Das Universum.” 2022. https://www.esa.int/kids/de/lernen/Unser_Universum/Geschichte_des_Universums/Das_Universum#:~:text=Dazu%20gehören%20Lebewesen%2C%20Planeten%2C%20Sterne,Millionen%20oder%20Milliarden%20Sterne%20enthält.
“Datavizcatalogue.” n.d. https://datavizcatalogue.com.
“Discovery Methods.” n.d. NASA. https://exoplanets.nasa.gov/alien-worlds/ways-to-find-a-planet/#.
Huber, Daniel. 2015. “Top 10 Potentially Habitable Exoplanets.” https://www.watson.ch/wissen/astronomie/578510805-das-sind-die-top-ten-der-exoplaneten-auf-denen-es-leben-geben-koennte.
Laboratory, NASAs Jet Propulsion. 2023. “Planets in Our Solar System.” NASA. https://solarsystem.nasa.gov/planets/overview/.
Libraries, Plotly Graphing. 2022. “Radar Charts in Python.” https://plotly.com/python/radar-chart/.
Lunar, and Planetary Institute. 2003. “Solar System Sizes.” NASA. https://solarsystem.nasa.gov/resources/686/solar-system-sizes.
———. 2023. “10 Need-to-Know Things about Venus.” NASA. https://solarsystem.nasa.gov/planets/venus/overview/.
“Planettypes.” 2022. https://exoplanets.nasa.gov/what-is-an-exoplanet/planet-types/overview/.
polsci. 2021. “Packed Circle Graph with Circlify, Matplotlib and Plotly.” https://gist.github.com/polsci/d9ecd38934f690ded5cd6ca061359814.
RenaudLN. n.d. “How to Subplot Radar Charts with 2 Traces Each.” https://community.plotly.com/t/how-to-subplot-radar-charts-with-2-traces-each/64440/2.
Singh, Harmanjot. 2020. “NASA Exoplanets Exploration Data.” https://www.kaggle.com/datasets/harmanjotsingh12js/nasa-exoplanets-exploration-data.
“The Habitable Zone.” 2021. https://exoplanets.nasa.gov/search-for-life/habitable-zone/.
“The Search for Life.” 2020. https://exoplanets.nasa.gov/search-for-life/why-we-search/.
Vicky Stein, Elizabeth Howell. 2022. “25 Weird and Wild Solar System Facts.” Future US Inc. https://www.space.com/35695-weirdest-solar-system-facts.html.
“Visualization Cumulative Exoplanets, by Method.” 2023. https://ourworldindata.org/grapher/cumulative-exoplanets-by-method.